170 ADVANCED PHYSIOLOGY 



seen in the living animal it shows distinct shrinking and en- 

 largement in size with each beat of the heart. The size of the 

 organ, too, would lead one to think that it must be of con- 

 siderable importance. In many animals it is as long as the 

 stomach itself, though not so broad. The use of the spleen is 

 not known. It can be entirely removed from the body without 

 fatal results. Various suggestions have been made as to its 

 functions; some think it concerned with the making of new 

 red blood corpuscles, while others take the opposite view, 

 that it is a place where old Corpuscles are destroyed. 



The Thyroid Glands. The thyroid glands are located, one 

 lobe on each side of the oesophagus, a little below "Adam's 

 apple/ ' or the voice box of the trachea ; see Fig. 98, page 178. 

 Their influence on the living processes in the body is much 

 more evident than that of the spleen. The material which 

 they pour into the blood has a very definite effect upon the 

 manner in which the blood nourishes different parts of the 

 body. If a person is born lacking these glands, there is, 

 apparently, a case of badly regulated nutrition; the child 

 grows up with a stupid brain, weak limbs and a misshapen 

 body a condition called cretinism. If such a child is given 

 a medicine containing the extract of the thyroid glands of 

 some animal, the trouble is frequently removed, the body 

 recovering its shape, and a normal development resulting. 

 The enlargement and disease of the thyroid glands sometimes 

 appears as great swellings on the neck, a trouble known as 

 goitre. 



Adrenal Bodies. Just above each kidney is located a small 

 gland, about the size of a walnut, called an adrenal body. 

 These bodies, too, empty their secretion into the blood as 

 it passes through them. While the amount of their secre- 

 tion in a given time is small, the fluid contributed is very 

 potent. Its main effect is to influence the muscles in the 

 walis of the arteries so that they contract and lessen the cali- 

 bre of the vessels. Under normal, healthy conditions, the 



